Soluble immune complexes have been found in sera of patients with many types of cancer and their presence and quantity has been related to prognosis and tumor burden, in a small selected group of patients with colon cancer, malignant melanoma and lung cancer. Preliminary characterization studies suggest that the complexes are relatively small (greater than 19S) and may be adsorbed to a protein A from staphylococci, a property associated mainly with IgG molecules. This proposal aims to evaluate whether fragment serial tests of sera from selected patients with leukemia, lung cancer, malignant melanoma and colon cancer will predict metastases or recurrence and, if so, to determine how soon in relation to other accepted clinical and laboratory tests the tests for immune complexes become positive. In addition we propose to characterize the molecules involved in immune complex formation and relate these to antigenic structures associated with tumor cells.